1. Field of the Invention
This invention relates to methods for contacting circuit chips, in particular circuit chips which have been attached to the surface of a support substrate.
2. Description of Prior Art
Chip cards without external contacts which use transponders for the transfer of energy and data are increasingly used in applications. Examples are the medical insurance card, bank cards, or credit cards which are currently still frequently equipped with contacts. The general trend is to build these cards using as thin a construction as possible. Currently, the usual thickness of the integrated circuits used in chip cards is still 150 xcexcm and above, with a trend towards the use of thinner chips of 100 xcexcm approximately being observable.
For current applications which go beyond chip cards and provide the combination of integrated circuits with paper or materials similar to paper, such as electronic labels, it would be advantageous to use circuit chips of a thickness markedly below 50 xcexcm, with the size striven for being approximately 10 xcexcm. Examples of such applications are described in DE 4432254, DE 19713799.7 or DE 19739474.4. The applications mentioned above have to be classed as belonging to the lower price sector, for which, however, huge numbers of such chip cards or electronic labels have to be manufactured in order to maintain the constant aim to minimize manufacturing costs.
There are currently no publications about the use of silicon chips of a thickness of less than 50 xcexcm. From multi-chip module applications it is known that chips are embedded in recesses in the support substrate. For this purpose, a recess is made in the support substrate, which may only be minimally larger than the chip to be embedded. Then the chip is inserted into the recess in the substrate. In order to ensure that chip and substrate surface are as flush as possible, both parts are laid with their upper surface downwards onto a plane glass plate. The gap between chip and substrate is then filled with a polymer, which, on the one hand, holds the chip in the recess and, on the other hand, produces a smooth transfer from the chip to the substrate on the upper surface. In this way, a quasi-planar surface is created. The connections between the chip and its surrounding are then achieved using thin film technology. In this way, further strip conductors, including conductors running across the chip, can be applied. The method described above is, however, much too costly and expensive for the mass production of transponder chips or electronic labels using the transponder technology.
A further possibility for the contacting of thin chips is the flip-chip connection technique. Using this technique the chip is soldered or glued with the active side downwards onto a corresponding connection area of the substrate. In order to assure a reliable contact, the connection areas are equipped with so-called bumps. These are metallic protuberances. However, the thickness of such a connection usually is markedly above 30 xcexcm, in most cases even above 50 xcexcm. In order to be able to make use of the advantages of a rather thin structure by use of the flip-chip connection technique, major developmental efforts to reduce the thickness of the connection joints would be required. For this purpose, the wafers are thinned from the back, for which they have to be attached to an auxiliary or intermediate support. In order to make the active side accessible for the flip-chip connection technique, a subsequent re-bonding on another intermediate support is required. The flip-chip connection technique is therefore, on the one hand, not suitable for producing a flat connection and, on the other hand, on account of the afore-mentioned difficulties arising from the re-bonding extensive.
DD 13 44 71 provides a method for connecting a semiconductor chip to support bodies, wherein an insulating layer is first formed on the support body. The insulating layer has a recess into which a semiconductor chip is subsequently inserted, in such a way that the surface of the semiconductor chip is flush with the surface of the insulating layer. The contact to the semiconductor chip is then made by screen printing onto the surface of the semiconductor chip and the surface of the insulating layer.
U.S. Pat. No. 5,155,068 A shows a method for the manufacture of an IC module for a chip card, wherein after its manufacture the IC module is inserted into a recess in the chip card.
DE 196 42 378 A1 describes a contactless chip card, with which a chip is located basically flush in a chip card substrate. In addition, on the chip card substrate, a coil structure is located in such a way that the same extends to the pads of the chip.
DE 44 31 606 A shows a chip card module, in which a chip is adhered into a recess in a support body, whereby the chip partially protrudes from the support body. Ends of a varnished wire coil located on the support body are soldered to the connection surfaces of the chip. From H. Wada, T. Kamijoh, IEEE J. of Selected Topics in QE, Vol. 3, No. 3, June 1997, pages 937-942, it is known that double heterostructures of an edge-emitting InP-InGaAsP laser applied to a silicon substrate by means of wafer bonding can show a small thickness in the region of for example 3 xcexcm.
It is the object of the present invention to provide methods by which, very cost effectively, in a single process, one the one hand, the electrical contacting of a thin circuit chip to the peripheral conductor structure can be made and, on the other hand, simultaneously, with the production of the peripheral conductor structure, the connections to the thin circuit chip are made.
According to a first aspect of the invention, this object is achieved by a method for contacting a circuit chip containing an integrated circuit of a thickness less than 50 xcexcm, which has at least two pads on its upper side, comprising the steps of:
placing the circuit chip with its underside onto a surface of a support substrate, in such a way that the entire thickness of the circuit chip protrudes from the surface of the support substrate; and
applying a structured metallic coating to the upper face of the circuit chip and to the surface of the support substrate by means of screen printing or stamping in order to connect the pads of the circuit chip to a conductor structure located on the upper surface of the support substrate.
According to a second aspect of the invention, this object is achieved by a method for contacting a circuit chip containing an integrated circuit of a thickness less than 50 xcexcm, which has at least two pads on its upper side, comprising the steps of:
placing the circuit chip with its underside onto a surface of a support substrate, in such a way that the entire thickness of the circuit chip protrudes from the surface of the support substrate; and
applying a structured metallic coating to the upper face of the surface chip and to the surface of the support substrate by means of screen printing or stamping in order to produce a peripheral conductor structure, which is connected to the pads of the circuit chip, on the surface of the support substrate and the upper side of the circuit chip.
The present invention is based on the knowledge that, when using thin circuit chips of thickness less than 50 xcexcm, preferably in a range from 10 to 20 xcexcm, it is possible to carry out a screen printing process or stamping for making contact to the pads located on the upper side of the circuit chip, even when the chip is placed on the upper surface of the support substrate. Therefore it is not necessary to sink the circuit chip into the support substrate by means of a costly process. Thereby the method according to the invention allows extremely cost effective manufacture of, for example, transponder modules for insertion into IC cards or electronic labels.
The method described can be applied especially advantageously to integrated circuits, i.e. circuit chips, with few pads, i.e. terminal areas, for example transponders with only two pads for the coil, since here at the lateral structural resolution no very great demands are being made because the coil printed simultaneously to the contacts does not exhibit a complex structure.
The methods according to the invention are advantageous especially with regard to economy and flexibility. For example, transponder modules can be manufactured in multiple printed panels and/or from roll to roll, with piece rates of several thousand per hour being possible. On account of the flatness of the finished structure, realized by means of the method according to the invention, it is possible without further consideration to laminate the structure into thin media such as paper. Therefore the thickness of today""s chip cards, which usually is approximately 0.7 mm, can be reduced to approximately 0.2 mm.
Further developments in the methods according to the invention are described in the dependent claims.